Method and device for receiving PTRS for cancelling phase noise in wireless communication system

ABSTRACT

A method for operating a user equipment in a wireless communication is provided as an embodiment of the present invention. The method may include: receiving modulation and coding scheme (MCS) information for each of two or more codewords from a base station (BS); determining a demodulation reference signal (DMRS) antenna port to which a phase tracking reference signal (PTRS) antenna port is mapped based on the MCS information; and receiving a PTRS based on the DMRS antenna port, wherein a DMRS antenna port with the lowest index among one or more DMRS antenna ports included in a codeword with the highest MCS among the two or more codewords may be determined as the DMRS antenna port.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/065,128, filed on Jun. 21, 2018, now U.S. Pat. No. 10,447,319, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2018/003455, filed on Mar. 23, 2018, which claimsthe benefit of U.S. Provisional Application No. 62/476,744, filed onMar. 25, 2017, 62/520,666, filed on Jun. 16, 2017, 62/525,775, filed onJun. 28, 2017, and 62/531,299, filed on Jul. 11, 2017, the contents ofwhich are all hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for receiving a phase tracking referencesignal (PTRS) for phase noise cancellation in a system and apparatustherefor.

BACKGROUND ART

An ultra-high frequency radio communication system using mmWave isconfigured to operate at a center frequency in the range of several GHzto several tens of GHz. Due to such a center frequency feature,significant path loss may occur in a shadow area in the mmWavecommunication system. Considering that a synchronization signal shouldbe stably transmitted to all user equipments (UEs) located withincoverage of a base station (BS), the synchronization signal needs to bedesigned and transmitted in consideration of the potential deep-nullphenomenon, which may occur due to the above-described ultra-highfrequency band characteristic, in the mmWave communication system.

DISCLOSURE OF THE INVENTION Technical Task

The present invention is contrived to solve the aforementioned problems.Accordingly, an object of the present invention is to provide a methodfor receiving a PTRS.

Another object of the present invention is to accurately decode receivedsignals by improving the phase noise cancellation procedure performed bya user equipment (UE) in a wireless communication system.

A further object of the present invention is to provide a method forimproving efficiency of signal transmission for phase noisecancellation.

Still another object of the present invention is to improvereceiving-side operation by providing information on signal transmissionfor phase noise cancellation.

Still a further object of the present invention is to provide a methodof transmitting a signal for phase noise cancellation by consideringphase noise compensation and reference signal overhead.

Technical Solutions

In an aspect of the present invention, provided herein is a method foroperating a user equipment (UE) in a wireless communication system. Themethod may include: receiving modulation and coding scheme (MCS)information for each of two or more codewords from a base station (BS);determining a demodulation reference signal (DMRS) antenna port to whicha phase tracking reference signal (PTRS) antenna port is mapped based onthe MCS information; and receiving a PTRS based on the DMRS antennaport, wherein a DMRS antenna port with the lowest index among one ormore DMRS antenna ports included in a codeword with the highest MCSamong the two or more codewords may be determined as the DMRS antennaport.

If the two or more codewords have the same MCS, a DMRS antenna port withthe lowest index among all DMRS antenna ports included in the two ormore codewords may be determined as the DMRS antenna port.

All DMRS antenna ports included in the two or more codewords may belongto one DMRS antenna port group.

If all DMRS antenna ports included in the two or more codewords belongto two or more DMRS antenna port groups, the number of PTRS antennaports may be equal to or less than the number of two or more DMRSantenna port groups.

The method may further include receiving information on the number ofPTRS antenna ports from the BS.

When all DMRS antenna ports included in the two or more codewords belongto the two or more DMRS antenna port groups, if the number of PTRSantenna ports is one, a DMRS antenna port with the lowest index amongone or more DMRS antenna ports belonging to a DMRS antenna port groupincluded in the codeword with the highest MCS among the two or morecodewords may be determined as the DMRS antenna port.

The method may further include: transmitting, to the BS, channel qualityinformation (CQI) for each of the two or more codewords; andtransmitting, to the BS, the layer index of a layer with the bestchannel quality among one or more layers included in a codewords withthe highest CQI among the two or more codewords.

In another aspect of the present invention, provided herein is a userequipment (UE) operating in a wireless communication system. The UEincludes: a transceiver configured to transmit and receive signals toand from a base station (BS); and a processor connected to thetransceiver, wherein the processor is configured to: receive modulationand coding scheme (MCS) information for each of two or more codewordsfrom the BS; determine a demodulation reference signal (DMRS) antennaport to which a phase tracking reference signal (PTRS) antenna port ismapped based on the MCS information; and receive a PTRS based on theDMRS antenna port, wherein a DMRS antenna port with the lowest indexamong one or more DMRS antenna ports included in a codeword with thehighest MCS among the two or more codewords may be determined as theDMRS antenna port.

Advantageous Effects

According to the present specification, received signals can beaccurately decoded by improving a phase noise cancellation procedureperformed by a user equipment (UE) in a wireless communication system.

According to the present specification, a method for improvingefficiency of signal transmission for phase noise cancellation can beprovided.

According to the present specification, receiving-side operation can beimproved by providing information on the signal transmission for thephase noise cancellation.

According to the present specification, a PTRS allocation method can beprovided.

According to the present specification, a method of transmitting asignal for the phase noise cancellation by considering compensation forphase noise and reference signal overhead can be provided.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present specification are not limitedto what has been particularly described hereinabove and other advantagesof the present invention will be more clearly understood from thefollowing detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 illustrates a method by which a UE transmits a layer indexaccording to an embodiment of the present invention.

FIG. 2 illustrates a method by which a UE receives a PTRS according toan embodiment of the present invention.

FIG. 3 illustrates a method for mapping PTRS ports to DMRS ports.

FIG. 4 illustrates a method for mapping PTRS ports to DMRS ports.

FIG. 5 is a diagram illustrating the configuration of a user equipmentand a base station according to an embodiment of the present invention.

BEST MODE FOR INVENTION

Although the terms used in the present invention are selected fromgenerally known and used terms, terms used herein may be varieddepending on operator's intention or customs in the art, appearance ofnew technology, or the like. In addition, some of the terms mentioned inthe description of the present invention have been selected by theapplicant at his or her discretion, the detailed meanings of which aredescribed in relevant parts of the description herein. Furthermore, itis required that the present invention is understood, not simply by theactual terms used but by the meanings of each term lying within.

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. In addition, some constituent componentsand/or characteristics may be combined to implement the embodiments ofthe present invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments asnecessary.

In describing the present invention, if it is determined that thedetailed description of a related known function or construction rendersthe scope of the present invention unnecessarily ambiguous, the detaileddescription thereof will be omitted.

In the entire specification, when a certain portion “comprises orincludes” a certain component, this indicates that the other componentsare not excluded and may be further included unless specially describedotherwise. The terms “unit”, “-or/er” and “module” described in thespecification indicate a unit for processing at least one function oroperation, which may be implemented by hardware, software or acombination thereof. The words “a or an”, “one”, “the” and words relatedthereto may be used to include both a singular expression and a pluralexpression unless the context describing the present invention(particularly, the context of the following claims) clearly indicatesotherwise.

In this specification, the embodiments of the present invention havebeen described based on a data transmission and reception relationshipbetween a mobile station and a base station. Here, the base station maymean a terminal node of the network which directly communicates with themobile station. In this document, a specific operation described asperformed by the base station can also be performed by an upper node ofthe base station.

That is, in the network consisting of a plurality of network nodesincluding the base station, various operations performed forcommunication with the mobile station may be performed by the basestation or other network nodes except the base station. The term “basestation” may be replaced with terms such as “fixed station”, “Node B”,“eNode B (eNB)”, “advanced base station (ABS)”, “access point”, etc.

The term “mobile station (MS)” may be replaced with terms such as “userequipment (UE)”, “subscriber station (SS)”, “mobile subscriber station(MSS)”, “mobile terminal”, “advanced mobile station (AMS)”, “terminal”,etc.

In addition, a transmitting end refers to a fixed and/or mobile nodethat transmits data or voice services, and a receiving end refers to afixed and/or mobile node that receive data or voice services.Accordingly, in uplink, the mobile station and base station maycorrespond to the transmitting end and receiving end, respectively.Similarly, in downlink, the mobile station and base station maycorrespond to the receiving end and transmitting end, respectively.

When a device performs communication with a ‘cell’, it may indicate thatthe device transmits and receive signals with a base station of thecell. That is, although the device actually transmits and receivessignals with a specific base station, it can be interpreted to mean thatthe device transmits and receives signals with a cell formed by thespecific base station. Similarly, “macro cell” and/or “small cell” maymean not only specific coverage but also “macro base station supportingthe macro cell” and/or “small cell base station supporting the smallcell”.

The embodiments of the present invention can be supported by standarddocuments disclosed in at least one of wireless access systems includingthe IEEE 802.xx system, 3GPP system, 3GPP LTE system, and 3GPP2 system.That is, the steps or parts, which are not explained to clearly revealthe technical idea of the present invention, in the embodiments of thepresent invention may be supported by the above documents.

In addition, details of all terms mentioned in the present document canbe found in the above standard documents. In particular, the embodimentsof the present invention can be supported by at least one of documentsP802.16e-2004, P802.16e-2005, P802.16.1, P802.16p and P802.16.1b, whichare standard documents for the IEEE 802.16 system.

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. It isto be understood that the detailed description which will be disclosedalong with the accompanying drawings is intended to describe theexemplary embodiments of the present invention and is not intended todescribe a unique embodiment for carrying out the present invention.

It should be noted that specific terms disclosed in the presentinvention are provided for better understanding of the present inventionand these specific terms may be changed to other terms without departingfrom the technical scope or spirit of the present invention.

According to an embodiment of the present invention, all layers may havethe same common phase error (CPE). In this case, a BS may transmit aphase tracking reference signal (PTRS) via a certain layer among aplurality of layers, which are configured for the BS, and each layer mayhave different reception quality (e.g., SNR or SINR). In this case, theBS transmits the PTRS via a layer (or DMRS port) with the highestquality to improve UE′ estimation performance. For example, a PTRSantenna port may be mapped to one DMRS port in one DMRS antenna portgroup. If a PTRS antenna port is mapped to a DMRS antenna port (orprecoding) with the best channel quality, CPE estimation performance maybe improved. However, to this end, separate signaling should be defined.Meanwhile, if an MCS is defined per codeword (CW), the BS/UE may knowwhich CW has the best quality. That is, based on the CW features, it ispossible to reduce signaling overhead required for indicating the DMRSantenna port (or precoding) with the best channel quality.

For example, in the case of downlink, a UE may report CQI every CW (orlayer group). The CW is composed of one or more layers. For example, inthe new radio (NR) system, up to two CWs are allowed, and the maximumnumber of layers in each CW may be set to 4. For example, if five layersare configured, CW #0 may have two layers, and CW #1 may have threelayers.

As another example, the two CWs may belong to one DMRS (antenna) portgroup. Alternatively, one CW may have two DMRS antenna port groups. Inother words, it is possible to define a layer group and a DMRS antennaport group in an independent manner

For example, when one DMRS antenna port group has two CWs, the BS mayknow which CW has a better quality by receiving CQI per CW. If the BSmaps a PTRS antenna port to one of DMRS antenna ports belonging to thebetter CW, the CPE estimation performance may be improved. Meanwhile,the UE may know the CW selected by the BS for PTRS mapping afterchecking the MCS of the CW. However, the UE cannot know which DMRSantenna port is mapped to the PTRS antenna port. To this end, thefollowing method may be considered.

As another example, when all DMRS antenna ports included in two or moreCWs belong to two or more DMRS antenna port groups and when the numberof PTRS antenna ports is one, a DMRS antenna port with the lowest indexamong one or more DMRS antenna ports included in a DMRS antenna portgroup(s) included in a CW with the highest MCS among the two or more CWsmay be determined as the DMRS antenna port.

FIG. 1 illustrates a method by which a UE transmits a layer indexaccording to an embodiment of the present invention.

Referring to FIG. 1, the UE may group a plurality of layers into two ormore layer groups [S110]. For example, in the LTE and NR system, up totwo layer groups (or CWs) may be allowed. Thereafter, the UE maytransmit channel quality information (CQI) for each of the two or morelayer groups (or CWs) to the BS [S120]. In the commercial communicationsystem (e.g., LTE, NR, etc.), the UE performs grouping of layers anddefines different CQI for each group. In addition, the UE may repot theCQI to the BS. In this case, the CQI report includes that a certainlayer group has a higher quality than other layer groups.

Next, the UE may transmit, to the BS, the layer index of a layer withthe best channel quality among one or more layers belonging to a layergroup with the highest CQI among the two or more layer groups [S130].

For example, the UE may select the layer with the highest quality fromthe layer group with the highest CQI and repot the selected layer to theBS. In this case, the UE may reduce overhead required for reporting thebest layer. For example, in the case of rank=7, two layer groups may bedefined, and the two layer groups may have three layers and four layers,respectively. If the CQI of the first layer group is better than that ofthe second layer group, the best layer may be selected from the firstlayer group. In this case, layers included in each layer group may beindexed from 0 in each layer group. Thus, when there are seven layers,three-bit overhead is required to inform the best layer. However, whenthe CQI is used, the amount of required overhead is reduced to two bits.That is, the overhead is reduced by one bit. In summary, if the UE usesthe CQI in reporting the layer with the highest quality to thetransmitter, the overhead may be reduced.

FIG. 2 illustrates a method by which a UE receives a PTRS according toan embodiment of the present invention.

Referring to FIG. 2, the UE may receive modulation and coding scheme(MCS) information for each of two or more CWs from the BS [S210]. Forexample, in the LTE and NR system, up to two layer groups (or CWs) maybe allowed.

For example, the BS may determine the MCS based on CQI for each of thelayer groups. In this case, the CQI-based determination means that theBS determines the MCS using the CQI for each layer group, but it mayalso means that the BS determines the MCS regardless of the CQI for eachlayer group.

When the BS determines the MCS using the CQI for each layer group, theBS may map DMRS antenna ports to PTRS antenna ports such that aplurality of layers belonging to the layer group (or CW) with thehighest CQI match the PTRS antenna ports.

For example, in 8-layer transmission, first and second CWs are defined,and it is assumed that the first CW is mapped to DMRS antenna ports #1to #4 and the second CW is mapped to DMRS antenna ports #5 to #8. Inthis case, if the CQI of the first CW is better than that of the secondCW, DMRS antenna ports #1 to #4 may correspond to PTRS antenna ports #11to #14. At this time, PTRS ports #11 to #14 may be alternatelytransmitted in the frequency domain. Alternatively, if the CQI of thesecond CW is better than that of the first CW, DMRS antenna ports #5 to#8 may correspond to PTRS antenna ports #11 to #14.

As another example, when the two CWs have the same CQI, the UE maypreferentially use a specific CW (e.g., the first CW) at all times. As afurther example, the UE may select a CW with more layers. In this case,it is expected that the spatial diversity will be relatively increased.Meanwhile, some of PTRS antenna ports #11 to #14 may be selected, andthen the selected PT-RS ports may be alternately transmitted in thefrequency domain. For example, if the number of PTRS antenna portsavailable for RRC is 2, only PTRS antenna ports #11 and #12 arealternately transmitted in the frequency domain.

In other words, the BS may group layers and define a different MCS foreach group. In this case, the BS may determine the layer grouping andthe MCS of each layer group based on layer grouping information and CQIreported by the UE. At this time, although the BS may use the groupinginformation and CQI reported by the UE as it is, it is not guaranteed.For the similar reasons, the BS may not transmit the PTRS via the bestlayer, which is recommended by the UE.

When transmitting layers, the BS may define a DMRS antenna port for eachlayer. Thus, in this case, it can be represented that PTRS antenna portsare mapped to layers, and more preferably, PTRS antenna ports are mappedto DMRS antenna ports. In addition, mapping of a PTRS antenna port to aDMRS antenna port may mean that the PTRS antenna port has the sameprecoder as that of the DMRS antenna port to which the PTRS antenna portis mapped. Moreover, the PTRS antenna port and DMRS antenna port may belocated at the same frequency location. In this case, the size (e.g.,norm 2) of the precoder may be different or equal.

As described above, the UE may determine the DMRS antenna port to whichthe PTRS antenna port is mapped [S220].

For example, the UE may determine the antenna port where a phasetracking reference signal (PTRS) is transmitted.

For example, when the BS maps a PTRS to be transmitted to a DMRS antennaport (or layer) with the best quality, the BS may explicitly inform theUE of the DMRS antenna port to which the PTRS antenna port is mapped. Inthis case, if the PTRS antenna port transmitted from the BS is mapped toone of DMRS antenna ports belonging to a CW with the highest MCS,signaling overhead may be reduced.

For example, in the case of rank=7, two CWs may be defined, and the twoCWs may have three DMRS antenna ports and four DMRS antenna ports,respectively. If the MCS of the first CW is higher than that of thesecond CW, the DMRS antenna port with the best quality may be selectedfrom among DMRS antenna ports belonging to the first CW. Thus, whenthere are seven DMRS antenna ports, three-bit overhead is required toinform the DMRS antenna port with the best quality. However, when theMCS is used, the amount of required overhead is reduced to two bits.That is, the overhead is reduced by one bit. In summary, if the BSinforms the UE of the index of the DMRS antenna port to which the PTRSantenna port is mapped, the overhead may be reduced based on the MCSinformation.

As another example, when two or more CWs have the same MCS, the antennaport index may indicate the antenna port included in the CW (e.g., CW#0) with the lowest index among antenna port groups.

As a further example, the PTRS may be received via an antenna port withthe lowest index among antenna ports included in a CW with the highestMCS among CWs.

For example, when the UE is scheduled with two CWs, the PTRS antennaport may be associated with a DMRS antenna port with the lowest indexamong DMRS antenna ports allocated for a CW with a higher MCS. If thetwo CWs have the same MCS, the PTRS antenna port may be associated witha DMRS antenna port with the lowest index allocated to CW #0.Alternatively, if the two CWs have the same MCS, the PTRS antenna portmay be associated with a DMRS antenna port with the lowest index amongall DMRS antenna ports included in the two CWs.

As another example, when the UE is scheduled with two CWs, the PTRSantenna port may be associated with a DMRS antenna port with the highestindex among DMRS antenna ports allocated for a CW with a higher MCS. Inaddition, if the two CWs have the same MCS, the PTRS antenna port may beassociated with a DMRS antenna port with the highest index allocated toCW #0. Alternatively, if the two CWs have the same MCS, the PTRS antennaport may be associated with a DMRS antenna port with the highest indexamong all DMRS antenna ports included in the two CWs.

Meanwhile, if a PTRS antenna port is associated with a DMRS antenna portgroup (1:M(>=1)), the CPE or phase shift estimation value, which iscalculated using the PTRS port, may be applied to all DMRS antenna portsbelonging to the DMRS antenna port group. In addition, if a PTRS antennaport is associated with a DMRS antenna port (1:1), the PTRS antenna portand DMRS antenna port use the same precoder, and they may be defined atthe same frequency location.

All DMRS antenna ports included in two or more CWs may belong to oneDMRS antenna port group, or they may belong to two or more DMRS antennaport groups. For example, if all DMRS antenna ports included in two ormore DMRS CWs belong to two or more DMRS antenna port groups, the numberof PTRS antenna ports may be equal to or less than the number of two ormore DMRS antenna port groups.

For example, when a DMRS antenna port group exists and one or two CWsexist, one PTRS antenna port may be defined. In this case, theabove-described embodiment may be applied. Meanwhile, when two DMRSantenna port groups exist and one or two CWs exists, two PTRS antennaports may be defined. The number of PTRS ports may be equal to or lessthan the number of DMRS antenna port groups. In this case, the number ofCWs does not affect the number of PTRS antenna ports. In addition, eachof the two PTRS antenna ports may be mapped to anyone among DMRS portsin each of the two DMRS antenna port groups. For example, each of thetwo PTRS antenna ports may be associated with a DMRS port with thelowest index among DMRS ports in each of the two DMRS antenna portgroups.

Moreover, the UE may receive information on the number of PTRS antennaports from the BS.

When transmitting a PTRS antenna port, the BS may map the PTRS antennaport to a DMRS antenna port with the lowest index among allocated DMRSantenna ports. This can be achieved if the BS allocates the DMRS antennaport with the lowest index to the layer with the best quality, which isreported by the UE. By doing so, in this case, the BS does not need toexplicitly inform the UE of the DMRS antenna port to which the PTRSantenna port is mapped.

Meanwhile, when the BS transmits two CWs to the UE, one or more DMRSantenna ports may be defined per CW. For example, in the case of rank=7,CW #0 may have DMRS antenna ports #0, #1, and #2, and CW #1 may haveDMRS antenna ports #3, #4, #5, and #6. If the PTRS port is mapped to aDMRS antenna port with the lowest index regardless of the MCS of eachCW, the following problem may occur. For example, according to thismapping scheme, if the MCS of CW #0 is lower than that of CW #1, thePTRS antenna port is mapped to a DMRS antenna port with a low MCS. Toovercome this problem, the PTRS antenna port should be mapped to a DMRSantenna port with the lowest index in a DMRS antenna port group with ahigh MCS.

For example, assuming that the UE reports column #3 of CW #0, the BS mayswitch between the location of the third column and the location of thefirst column. In other words, a DMRS antenna port corresponding to thefirst precoding may have the best quality. Therefore, the BS may map thePTRS antenna port to the DMRS port corresponding to the first column(precoding) at all times. In this case, the BS does not need to informthe UE of the DMRS antenna port to which the PTRS antenna port ismapped.

Thereafter, the UE may receive the PTRS based on the determined DMRSantenna port [S230].

FIGS. 3 and 4 illustrate a method for mapping PTRS ports to DMRS ports.

Referring to FIG. 3, in one CW, a PTRS may be associated with a DMRSantenna port with the lowest index in a DMRS antenna port group. Forexample, in FIG. 3, if the DMRS antenna port group is composed of DMRSantenna ports #0, #1, and #2, the PTRS antenna port may be associatedwith DMRS antenna port #0. However, when two CWs are applied asdescribed above, a DMRS port to which the PTRS needs to be mapped shouldbe determined. For example, it is assumed that the first CW (CW #0)corresponds to DMRS ports {#0, #1} and the second CW (CW #1) correspondsto DMRS ports {#2, #3, #4}. In this case, for example, if the PTRS ismapped to a DMRS antenna port belonging to a CW with a higher MCS, it isexpected that the performance will be improved. In other words, the PTRSneeds to be matched with the DMRS antenna port belonging to the CW thehigher MCS. In this case, the BS (e.g., gNB) may select a CW that can bemapped to the PTRS base on CQI reported by the UE. In this case,additional gains can be determined according to Equation 1 byconsidering CPE performance improvement.Additional gain=1.8 dB×CQI difference between two CWs  [Equation 1]

In this case, as another example, two CWs may be used as shown in FIG.4. In this case, for example, if a UE is allocated rank 5 or more, twoCWs may be used. At this time, a PTRS may be associated with a DMRSantenna port with the lowest index in a CW with the highest MCS.

For example, referring to FIG. 4, the first CW (CW #0) may be matchedwith DMRS antenna ports {#0, #1}, and the second CW (CW #1) may bematched with DMRS antenna ports {#2, #3, #4}.

In this case, the MCS of the second CW is higher than that of the firstCW (or when the CQI of the second CW is higher than that of the firstCW), the PTRS port may be associated with a DMRS antenna port with thelowest index in the second CW. That is, the PTRS port may be associatedwith DMRS antenna port #2. By doing so, the CPE estimation performancemay be improved based on the PTRS without any signaling overhead.

In addition, for example, in the case of downlink, the UE may report thebest layer in a specific CW. In this case, the UE selects a layercorresponding to a CW with high CQI for a downlink PTRS and reports itto the BS via the selected layer, thereby reducing reporting bits. Forexample, uplink control information (UCI) feedback bits may be decreasedfrom 3 bits to 2 bits.

Moreover, in the case of uplink, the UE may transmit an uplink PTRS tothe BS via the best layer. The BS may inform the UE of a layer to beused for uplink PTRS transmission through DCI. In this case, if a layercorresponding to a CW with a high MCS is selected as described above,the number of bits in a corresponding field included in DCI may bereduced. However, the present invention is not limited thereto.

FIG. 5 is a diagram illustrating the configuration of a user equipmentand a base station according to an embodiment of the present invention.In FIG. 5, the user equipment 100 and the base station 200 may includeradio frequency (RF) units 110 and 210, processors 120 and 220 andmemories 130 and 230, respectively. Although FIG. 5 shows a 1:1communication environment between the user equipment 100 and basestation 200, a communication environment may be established between aplurality of user equipments and a base station. In addition, theconfiguration of the base station 200 shown in FIG. 5 can be applied toa macro cell base station and a small cell base station.

The RF units 110 and 210 may include transmitters 112 and 212 andreceivers 114 and 214, respectively. The transmitter 112 and thereceiver 114 of the user equipment 100 are configured to transmit andreceive signals to and from the base station 200 and other userequipments, and the processor 120 is functionally connected to thetransmitter 112 and the receiver 114 to control processes performed atthe transmitter 112 and the receiver 114 for transmitting and receivingsignals to and from other devices. The processor 120 processes a signalto be transmitted, sends the processed signal to the transmitter 112,and processes a signal received by the receiver 114.

If necessary, the processor 120 may store information included in anexchanged message in the memory 130. Due to this structure, the userequipment 100 can perform the methods described in various embodimentsof the present invention.

The transmitter 212 and the receiver 214 of the base station 200 areconfigured to transmit and receive signals to and from another basestation and user equipments, and the processor 220 is functionallyconnected to the transmitter 212 and the receiver 214 to controlprocesses performed at the transmitter 212 and the receiver 214 fortransmitting and receiving signals to and from other devices. Theprocessor 220 processes a signal to be transmitted, sends the processedsignal to the transmitter 212, and processes a signal received by thereceiver 214. If necessary, the processor 220 may store informationincluded in an exchanged message in the memory 230. Due to thisstructure, the base station 200 can perform the methods described invarious embodiments of the present invention.

The processors 120 and 220 of the user equipment 100 and the basestation 200 instruct (for example, control, adjust, or manage) operationof the user equipment 100 and the base station 200, respectively. Theprocessors 120 and 220 may be connected to the memories 130 and 230 forstoring program code and data, respectively. The memories 130 and 230are respectively connected to the processors 120 and 220 so as to storeoperating systems, applications and general files.

Each of the processors 120 and 220 of the present invention may becalled a controller, a microcontroller, a microprocessor, amicrocomputer, etc. Each of the processors 120 and 220 may beimplemented by hardware, firmware, software, or any combination thereof.

When the embodiments of the present invention are implemented byhardware, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), and the like may be included in the processors 120 and 220.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code may be stored ina memory unit and be then executed by a processor. The memory unit maybe provided within or outside the processor to exchange data with theprocessor through the various means known to the public.

As mentioned in the foregoing description, the detailed descriptions forthe preferred embodiments of the present invention are provided to beimplemented by those skilled in the art. While the present invention hasbeen described and illustrated herein with reference to the preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and variations can be made therein withoutdeparting from the spirit and scope of the invention. Therefore, thepresent invention is non-limited by the embodiments disclosed herein butintends to give a broadest scope matching the principles and newfeatures disclosed herein. In addition, although the present inventionhas been described with reference to the preferred embodiments thereof,it will be apparent to those skilled in the art that not only theinvention is not limited to the aforementioned specific embodiments butvarious modifications can be made in the present invention withoutdeparting from the spirit or scope of the invention. Such modificationsare not to be construed individually from the technical spirit and scopeof the present invention.

In addition, both an apparatus invention and a method invention areexplained in the present specification, and if necessary, theexplanation on both the inventions can be complementally applied.

INDUSTRIAL APPLICABILITY

The above-described method can be applied to not only the 3GPP systembut also various wireless communication systems including an IEEE802.16x system and an IEEE 802.11x system. Further, the proposed methodcan also be applied to an mmWave communication system using ultra highfrequency band.

What is claimed is:
 1. A method for operating a user equipment (UE) in awireless communication system, the method comprising: receivingmodulation and coding scheme (MCS) information for each of two codewordsfrom a base station (BS); based on the received MCS information,determining a demodulation reference signal (DMRS) antenna port, among aplurality of DMRS antenna ports, to which a phase tracking referencesignal (PTRS) antenna port has been mapped; and receiving a PTRS via thePTRS antenna port, wherein, in a case where the two codewords have adifferent MCS, the PTRS antenna port has been mapped to a DMRS antennaport with the lowest index among one or more DMRS antenna ports for acodeword with the highest MCS among the two codewords, and wherein, in acase where the two codewords have the same MCS, the PTRS antenna porthas been mapped to a DMRS antenna port with the lowest index among theplurality of DMRS antenna ports for the two codewords.
 2. The method ofclaim 1, wherein all DMRS antenna ports related to the two codewordsbelong to one DMRS antenna port group.
 3. The method of claim 1, whereinthe PTRS antenna port has at least one of subcarrier indexes configuredfor the DMRS port to which the PTRS antenna port has been mapped.
 4. Themethod of claim 1, wherein the PTRS antenna port and the DMRS port towhich the PTRS antenna port has been mapped have the same precoding. 5.The method of claim 1, further comprising: transmitting, to the BS,channel quality information (CQI) for each of the two codewords; andtransmitting, to the BS, information on layer index of a layer with thebest channel quality among one or more layers included in a codewordswith the highest CQI among the two codewords.
 6. The method of claim 1,wherein the UE receives the PTRS via the PTRS antenna port, based on thedetermination.
 7. A user equipment (UE) operating in a wirelesscommunication system, the UE comprising: a transmitter; a receiver; atleast one processor; and at least one computer memory operablyconnectable to the at least one processor and storing instructions that,when executed by the at least one processor, perform operationscomprising: receiving modulation and coding scheme (MCS) information foreach of two codewords from a base station (BS); based on the receivedMCS information, determining a demodulation reference signal (DMRS)antenna port, among a plurality of DMRS antenna ports, to which a phasetracking reference signal (PTRS) antenna port has been mapped; andreceiving a PTRS via the PTRS antenna port based on the determination,wherein, in a case where the two codewords have a different MCS, thePTRS antenna port has been mapped to a DMRS antenna port with the lowestindex among one or more DMRS antenna ports for a codeword with thehighest MCS among the two codewords, and wherein, in a case where thetwo codewords have the same MCS, the PTRS antenna port has been mappedto a DMRS antenna port with the lowest index among the plurality of DMRSantenna ports for the two codewords.
 8. The UE of claim 7, wherein allDMRS antenna ports related to the two codewords belong to one DMRSantenna port group.
 9. The UE of claim 7, wherein the PTRS antenna porthas at least one of subcarrier indexes configured for the DMRS port towhich the PTRS antenna port has been mapped.
 10. The UE of claim 7,wherein the PTRS antenna port and the DMRS port to which the PTRSantenna port has been mapped have the same precoding.
 11. The UE ofclaim 7, the operations further comprising: transmitting, to the BS,channel quality information (CQI) for each of the two codewords; andtransmitting, to the BS, information on layer index of a layer with thebest channel quality among one or more layers included in a codewordswith the highest CQI among the two codewords.
 12. The UE of claim 7,wherein the UE receives the PTRS via the PTRS antenna port, based on thedetermination.
 13. A base station (BS) operating in a wirelesscommunication system, the BS comprising: a transmitter; a receiver; atleast one processor; and at least one computer memory operablyconnectable to the at least one processor and storing instructions that,when executed by the at least one processor, perform operationscomprising: transmitting to a user equipment (UE), modulation and codingscheme (MCS) information for each of two codewords; transmitting to theUE, a phase tracking reference signal (PTRS) via a PTRS antenna port,wherein the PTRS antenna port is mapped to a demodulation referencesignal (DMRS) antenna port, among a plurality of DMRS antenna ports,wherein, in a case where the two codewords have a different MCS, thePTRS antenna port is mapped to a DMRS antenna port with the lowest indexamong one or more DMRS antenna ports for a codeword with the highest MCSamong the two codewords, and wherein, in a case where the two codewordshave the same MCS, the PTRS antenna port is mapped to a DMRS antennaport with the lowest index among the plurality of DMRS antenna ports forthe two codewords.
 14. The BS of claim 13, wherein all DMRS antennaports related to the two codewords belong to one DMRS antenna portgroup.
 15. The BS of claim 13, wherein the PTRS antenna port has atleast one of subcarrier indexes configured for the DMRS port to whichthe PTRS antenna port is mapped.
 16. The BS of claim 13, wherein thePTRS antenna port and the DMRS port to which the PTRS antenna port ismapped have the same precoding.
 17. The BS of claim 13, the operationsfurther comprising: receiving from the UE, channel quality information(CQI) for each of the two codewords; and receiving from the UE,information on layer index of a layer with the best channel qualityamong one or more layers included in a codewords with the highest CQIamong the two codewords.